This invention concerns a method for producing a pattern on a transparent substrate, particularly a glass or glass-ceramic substrate, and also a substrate produced by this method.
It is well known from the prior art to use enamels to produce a decorative pattern on a glass or glass-ceramic substrate.
The enamels used for this application are generally obtained from what is known as an enamel composition, comprising a powder essentially composed of at least one glass frit (which acts as a vitreous matrix) and pigments as colorants in particular, the glass frit and the pigments being metal-oxide-based, and a medium permitting the application of the enamel composition to the substrate and its temporary adhesion thereto. The medium selected, depending on the intended use of the enamel, must ensure the satisfactory placing in suspension of the frit particles and pigment particles used and must be consumed during the baking of the enamel. This medium can include solvents, diluents, oils, resins, etc.
It is known to deposit these enamels by various printing techniques, most particularly by screen-printing techniques using a fabric whose mesh count and mesh openings depend on the pattern to be produced. These printing techniques are very advantageous from an economic point of view, in that they can be used for high-speed mass production. In addition, they are very well suited to the reproduction of large-sized decorative patterns on substrates of the types used by glassmakers.
These techniques are not completely satisfactory, however, particularly in terms of flexibility of use and esthetics.
First, in order to change the pattern for reproduction it is necessary to change the screen-printing cloth, which is tedious in industrial operations, especially in "personalized" small-series production.
Second, the screen-printing technique itself leaves a grid that betrays the original visible in the decorative pattern. Visually, the substrate provided with the gridded pattern has something of the appearance of a piece of fabric.
It is also known from the prior art, for decorative applications on a substrate made of any desired material, particularly the formation of a colored visible image, to use photosensitive resins as vehicles for pigments or colorants.
For such applications, it is known to employ two different approaches to the use of these photosensitive resins.
The first approach consists in incorporating the desired ingredient (pigment or colorant) directly into the composition containing the photosensitive resin, then exposing the resin through a positive or negative plate by means of a UV lamp, and finally stripping it with an appropriate solvent to produce an insoluble image containing said ingredient on the substrate.
Moreover, this stripping step is cumbersome and complex, especially since it is necessary to find a perfect affinity between the solvent used and the resin and to master the operating conditions, especially with respect to duration.
The second approach consists in first exposing the photosensitive resin in the same manner as above, then causing the pigment(s) to be absorbed directly by the portions of said resin not exposed to light, and finally stripping the resulting system with an appropriate solvent.
Apart from the fact that these two approaches have in common that they are not suitable for large decorative patterns, most particularly because it is difficult to achieve an even distribution of the pigments over the entire surface of the substrate, they also have the major disadvantage of not yielding long-lasting products, since the pigments or colorants tend to separate from the substrate.